Forgotten Minerals #2: Caliche

What happens when you find a perfect substitute for a scarce resource? You carry on mining the scarce resource!

Glance at a satellite map image of María Elena, an old mining town in the Chilean desert, and two things leap out.

The first is the strange way the streets are laid out, almost like the lines on the Union Jack. This is because they were indeed designed to look like the Union Jack, a tribute to the fact that much of the industry here in Chile used to be financed by Britain.

The second thing that leaps out is that the town is surrounded on all sides by an extremely bizarre topographical feature unlike anything you’ve probably seen before. Instead of a flat desert landscape, eroded by the wind, you see hundreds of little ridges running perpendicular to each other for miles, all the way into the distance.

These ridges, and the enormous pile of waste rock to the north of the town, are a testament to what this town exists for: mining. Specifically, Maria Elena was the epicentre for one of the most important businesses in the world. This was where much of the world’s mineral nitrates were mined.

What those ridges look like up close. Well, from a drone…

A short history of nitrates

The story of nitrates is recounted at length in *Material World* - so feel free to skip the next bit if you’ve already read it - but in brief, it goes something like this. Back in the 18th century, the great and the good began to fret about an impending demographic crisis - the crisis Thomas Malthus became famous for. The population was growing but our ability to feed ourselves was limited by the ability of the soil to carry food. This was, to put it lightly, a Very Big Deal.

One way to increase the carrying capacity of the planet would be to find more fertiliser to help grow more crops but getting hold of fertilisers was, up until the mid-19th century, fiendishly difficult. In particular, getting hold of nitrogen was very hard indeed.

Nitrogen is, alongside potassium and phosphates, one of the three key plant nutrients (NPK). But of these three, nitrogen is by far the most important - the agent of biological growth that helps crops flourish. Moreover, nitrogen is also the critical ingredient in explosives. But for all that it is the most plentiful gas in the earth's atmosphere, there is, or rather was, no easy way of getting hold of the physical, solid or liquid nitrogen you might want to sprinkle on fields. So, for most of human history we have had to make do with "organic" fertiliser, which is to say animal manure.

But in the mid-19th century, Europeans discovered a set of islands off the coast of Peru called the Chincha islands. These were uninhabited bird colonies with an unusual feature. Because of the dry climate on the Pacific coast of South America, the birds’ droppings had built up over thousands of years, lithifying into a deep strata of what became known as “guano”.

The Chincha Islands. Image from Wikipedia

And guano, it so happened, was a rich source of nitrogen, phosphates and potassium. It was, in other words, the answer to everyone's prayers.

So: cue a mad rush for the guano - a bone fide gold rush (poo rush)? Tonnes of droppings was shipped around Cape Horn to Europe - and within a few decades it was gone. Exhausted - at least until, in a few hundred years the birds have produced enough droppings to create new layers all over again.

However, shortly after this geologists realised there was an even more plentiful source of mineral nitrogen to be found in the Atacama desert, across on the mainland. Caliche, as the source of this nitrogen became known, isn't a relation of guano - it's a mineral rather than a fossilised bird dropping. But, like guano this rock is rich in the nitrogen you need for fertilisers and explosives (it would spark if hit hard with something metal) and, like guano, it was only found in large quantities in this part of South America.

So the guano gold-rush was followed by the caliche gold-rush. Wars were fought over the rock (wars of great consequence, as it happens, but sorry, you really *will* have to read the book for more on that). And Chile rapidly became one of the wealthiest countries in Latin America. Towns like Maria Elena were constructed and capital flowed in, from dynasties like the Guggenheims, who staked their future on the caliche trade.

Which brings us back to those strange ridges stretching all the way into the distance as you drive in and out of María Elena. These are the piles of waste rock left behind when, nearly a century ago, the earliest diggers began scraping away the surface of the land in search of caliche. I’m not sure how long they will stay there, but perhaps the same South American climate that helped preserve the guano on the Chincha Islands will also preserve these odd ridges, so thousands of years from now, future civilisations try to work out what happened here, like today’s archaeologists puzzles over the Nasca lines further north in Peru.

Because in the first decades of the 20th century, along came an innovation that, in the world of nitrates at least, changed everything: the Haber Bosch process. Helped by Carl Bosch, Fritz Haber came up with a way of doing what everyone up until then had struggled to do: he turned atmospheric nitrogen into the physical stuff you can sprinkle on the ground. It was arguably the single biggest scientific discovery of the modern era. And it meant all of a sudden there was a nearly limitless substitute for the rocks in the ground here at María Elena.

The Conventional wisdom about caliche

And that brings us to the conventional wisdom about the caliche trade, which is, in short, that it is a historical artefact. Most of the miners are gone. The gold rush is over.

María Elena isn’t quite abandoned, but driving around it feels a little eerie. When I visited there a few years ago, a guest of SQM, the lithium mining company, we stayed in the old Guggenheim Residence, which is very charming, if somewhat less grand than you might have thought from the name. The whole place feels like it’s from another era - which, of course, it is.

Flicking through the guestbook I discovered, a few pages back, that another person to have stayed there was none other than Fidel Castro, in the 1970s.

On the north side of the town is the old Guggenheim caliche refinery. It was abandoned some years ago and, when I visited at least, was shrouded with fog - the camanchaca that comes in from the Pacific across the desert. The effect was to give it a woebegone appearance.

Some distance away on the highway, past miles and miles of those old ridges of discarded rock, is an abandoned mining town, Pedro de Valdivia. It’s an eerie place, the homes still left more or less as they were when the residents abandoned it. It’s a little like an old Wild West set, there in the middle of the desert, a testament to a bygone era when caliche came out of the ground here and helped feed the world.

But here’s the thing about that conventional wisdom about caliche: it’s not quite accurate. Because while caliche mining certainly isn’t talked about as much as it was a century ago, it turns out it hasn’t stopped. On the contrary, in 2023, Chile was still mining more than 720,000 tonnes of caliche - comfortably more than for most of the 1970s, back when Fidel Castro visited.

Why? Because - this is a lesson you’ll hear a lot in this series - once we start mining something, we humans very, very rarely ever stop. In the case of caliche, those ghost towns are mostly a testament to the fact not that mining has stopped, but that it no longer employs half as many people.

Further down the road at the Coya Sur refinery, SQM is turning out enormous quantities of mineral nitrates, much as the Guggenheims did here a century ago. What’s changed, aside from the number of people working here, is that they are using far more advanced processes to squeeze ever more minerals out of the caliche. The old Guggenheim plant, which boiled and bubbled the rocks, has been replaced by heap leaching systems and by advanced plants - massive juddering towers turning out millions of prills - the little ball-bearing sized particles of fertiliser, which will be shipped around the world to be sprinkled on fields.

According to the conventional wisdom, this place shouldn’t really exist. There is a perfect synthetic substitute for the nitrogen made here. The Haber Bosch process should have killed the caliche business. And it certainly accounts for the vast, vast majority of nitrogen produced around the world.

Yet the key thing about this chart - the thing that’s often ignored - is that the old fashioned mined stuff never went away. Look very closely at the black. Yes it’s piddling in comparison with the blue. But it’s still there. Somehow, by cutting costs and improving their efficiency, the caliche mines are still running.

In one respect, you might find this a little depressing. The desert is still being carved up by diggers and caliche ripped out from the surface - long after it was supposed to have been innovated out of existence. But now ponder how those Haber Bosch plants actually work. They take hydrogen out of gas or (in many Chinese plants) coal and use it to fix nitrogen from the air. In the process they are responsible for significant greenhouse gas emissions. In practice, this old fashioned mineral way of getting fertiliser is - even once you take account of all the trucks and energy used in the Chilean desert - more environmentally friendly than the modern methods that didn’t quite displace it.

But it turns out caliche is far from the only forgotten material we’re still mining plenty of, decades after we were supposed to have stopped. The next substance in this series is, if you can believe it, even more noxious and pollutive than the much-maligned greenhouse gases. Yet we still mine it in astounding quantities. For better or worse, the human appetite for minerals and mining rarely diminishes.